The treatment of a number of medical conditions requires the placement of catheters within a patient's blood vessel for an extended period of time. These long-term applications include blood access for hemodialysis, chemotherapy, parental nutrition, blood transfusions and blood sampling.
Vascular access with catheters was first introduced more than 20 years ago. With the advent of soft, flexible silicone double lumen catheters, both acute and chronic hemodialysis became a routine procedure. Although subclavian dialysis catheters are easily inserted and well tolerated, catheter lifespan averages about three months. This is of great concern to patients on maintenance dialysis.
It is well known in the medical field that chronic placement of a catheter in a patient's blood vessel often results in catheter failure due to aspiration of the blood vessel wall into the tip of the catheter, clot or thrombus formation at the tip of the catheter, or stenosis around the tip of the catheter. A catheter failure resulting from one or more of these mechanisms is evidenced by an inability to aspirate and/or infuse fluid through the catheter, generally referred to as catheter occlusion. Typically, catheter occlusions caused by aspiration of the blood vessel wall or clot formation at the catheter tip may be resolved by repositioning the catheter tip or infusing antithrombotic agents.
Stenosis is a narrowing of the blood vessel lumen as seen in a venogram and, in general, can be due to either the formation of a thrombus within the blood vessel or a thickening of the blood vessel wall. The generally accepted view is that stenosis around the tip of a catheter implanted within a blood vessel is due to the formation of a thrombus resulting from a biochemical reaction to the introduction of a foreign material into the blood vessel. Previous attempts to prevent catheter occlusion have centered around thromboresistant coatings on the catheter surface in order to prevent the biochemical reaction of the patient's blood to the material of which the catheter is formed.
Prior art related to the present invention deals with the placement of stents within a diseased blood vessel to treat the problems associated with stenosis. Stents range from simple wire meshes used in U.S. Pat. No. 4,800,882, to a canister made of hydrophilic plastic which expands upon placement in a blood vessel as in U.S. Pat. No. 4,434,797. Stents are typically secured to a deployment catheter for insertion into the patient's blood vessel via a percutaneous procedure. Surgical placement of these stents is achieved by feeding the catheter from a distant site, e.g., a percutaneous puncture into the femoral artery, to the stenosis target. The deployment catheter is then removed, leaving the stent within the blood vessel lumen.
Prior publications on the subject of mounting devices in the blood stream include "Registration of Phoric Changes of Blood Flow by Means of a Catheter-Type Flowmeter," by Heinz Pieper printed in The Review of Scientific Instrument 29(11):965-967, November 1958, and U.S. Pat. Nos. 4,425,908; 4,936,823; 4,813,930; 5,135,517; and 4,654,028. However, none of these address and solve the problems presented in the field of the present invention.